1. Field of the Invention
The present invention relates to insulating thick film compositions used for solder resists, materials for reinforcing strength, materials for adjusting density, materials for reducing irregularities, and the like, to ceramic electronic devices using the insulating thick film compositions, and to electronic apparatuses provided with the ceramic electronic devices.
2. Description of the Related Art
In recent years, the trends toward miniaturization and higher performance of electronic apparatuses, such as mobile communication apparatuses, are realized primarily by higher performances of semiconductor devices, such as LSIs, and by three-dimensional wiring and by wiring of higher densities on substrates mounting the semiconductor devices thereon. Ceramic substrates mounting various semiconductor devices are specifically required to be capable of connecting multi-terminals with narrower pitches, to have higher wiring density and to perform signal processing at higher frequencies. In particular, in response to the trend toward multi-terminals with narrower pitches, ceramic substrates are provided with a number of fine solder lands on major surfaces thereof.
However, when ceramic capacitors, semiconductor devices and the like are mounted by soldering on substrates, the locations at which soldering is performed are likely to deviate from the finer corresponding solder lands. In addition, when the solder is melted, it extends to undesirable areas at which soldering is not required due to wet spreading of the solder, and soldering defects and variation in characteristics may occur in some cases.
In order to prevent the wet spreading of solder, a method is known in which a solder resist layer is formed by a step of coating a resist resin which has poor wettability to solder on areas at which soldering is not required, and a step of curing the coated resin.
However, a ceramic substrate (in particular, a multilayer ceramic substrate) formed by baking a conductive pattern together with a laminate composed of green ceramic sheets tends to be warped and distorted due to the shrinkage during baking. Accordingly, locations of the conductive pattern may be varied, and thereby locations at which solder resists are coated may deviate from the designed points in some cases. This phenomenon is frequently observed in a high density mounting substrate having a number of fine solder lands thereon.
In order to solve the problem described above, for example, as disclosed in Japanese Unexamined Patent Application Publication No. 11-251723, when a ceramic substrate is formed by a step of coating an insulating paste composed of a powdered ceramic mixed with a glass component, as an overcoat layer on a green ceramic body having a surface conductive pattern, and a step of baking the insulating paste together with the ceramic substrate, relative positional accuracy between the surface conductive pattern and the overcoat layer can be improved.
However, since the insulating paste described above is composed of the glass component as an auxiliary agent for sintering and the powdered ceramic, the glass component diffuses to the ceramic substrate in baking and may adversely influence the sintering characteristics of the ceramic substrate in some cases. For example, since an area at which the overcoat is formed has the glass component at a concentration higher than that of an area at which the overcoat is not formed, the sintering behavior of the ceramic substrate may partly change. As a result, the generation of warping and undulation of the ceramic substrate may occur, and in addition, due to a reaction between the substrate and the glass, degradation in electrical characteristics may partly occur, and pores may be formed in some cases. Furthermore, the glass component in the overcoat layer may localize on the surface of the conductive pattern, and hence, the soldering characteristics and the plating characteristics may be degraded in some cases.
In consideration of the problems described above, the present invention was made. Accordingly, it is an object of the present invention to provide an insulating thick film composition baked together with a green ceramic body which can suppress the generation of warping and undulation of the green ceramic body caused by baking and which can better ensure the superior electrical characteristics. Another object of the present invention is to provide a ceramic electronic device formed by using an insulating thick film composition. In addition, a still another object of the present invention is to provide an electronic apparatus formed by using such ceramic electronic device.
The present invention relates to an insulating thick film composition which is baked together with a green ceramic body and comprises a powdered ceramic having the same composition system as that of a powdered ceramic contained in the green ceramic body, wherein the mean particle diameter of the powdered ceramic in the insulating thick film composition is smaller than that of the powdered ceramic contained in the green ceramic body.
In addition, the present invention relates to a ceramic electronic device formed by steps of forming a layer composed of an insulating thick film composition on a green ceramic body having a predetermined conductive pattern and baking the layer together with the green ceramic body, wherein the insulating thick film composition is an insulating thick film composition according to the present invention described above.
Since the insulating thick film composition of the present invention comprises a powdered ceramic having the same composition system as that of the powdered ceramic contained in the green ceramic body and since the mean particle diameter of the powdered ceramic in the insulating thick film composition is smaller than that of the powdered ceramic contained in the green ceramic body, superior electrical characteristics and dimensional stability of the green ceramic body can be satisfactory ensured.
In the present invention, xe2x80x9cthe same composition systemxe2x80x9d means that the powdered ceramic in the insulating thick film composition comprises at least one constituent component of the powdered ceramic contained in the green ceramic body. For example, when the powdered ceramic contained in the green ceramic body is a BaOxe2x80x94Al2O3xe2x80x94SiO2-based ceramic, the powdered ceramic in the insulating thick film composition may contain at least one of BaO, Al2O3, and SiO2.
In addition, since the ceramic electronic device of the present invention is a ceramic electronic device formed by the steps of coating the insulating thick film composition of the present invention on the green ceramic body having a predetermined conductive pattern and baking the coated insulating thick film composition together with the green ceramic body, a compact electronic device can be produced having superior electrical characteristics, dimensional stability and high performances. That is, a compact and highly reliable electronic apparatus having higher performances can be produced by using the electronic device of the present invention.